Film-recording cathode ray tube with open slit in a face-plate mounted film guiding vacuum frame



Sept. 12, 1967 R. A. FOTLAND FILM-RECORDING CATHODE RAY TUBE WITH OPEN SLIT IN A FACE-PLATE MOUNTED FILM GUIDING VACUUM FRAME Filed Aug. 4. 1966 FIG. 3.

INVENTOR R ichord A. Fat land ATTORNEY United States Patent f FILM-RECORDING CATHODE RAY TUBE WITH OPEN SLIT IN A FACE-PLATE MOUNTED FILM GUIDING VACUUM FRAME Richard A. Fotland', Lyndhurst, Ohio, assignor to Horizons Incorporated, a corporation of New Jersey Filed Aug. 4, 1966, Ser. No. 570,198 1 Claim. (Cl. 31374) ABSTRACT OF THE DISCLOSURE An evacuated cathode ray tube provided with a face plate having a vacuum frame surrounding a slit in the face plate and means to direct an electron beam to said slit and onto a recording medium pulled past the slit.

This application is a continuation-in-part of my copending United States patent applications Serial Number 414,963, filed December 1, 1964, now abandoned, and Serial Number 469,139, filed July 2, 1965.

This invention relates to the recording of electrical signals having bandwidths in the megacycle region. More particularly, it relates to the recording of electrical signals by modification of conventional cathode ray tube devices so that the electron beam strikes an electron sensitive medium directly without any intervening face plate in the cathode ray tube.

One form of conventional electron beam recording employs an evacuated cathode ray tube having means to deflect, focus and modulate an electron beam. The tube is usually constructed with a face plate supporting a phosphor which serves to convert the electron energy into radiant energy. Such cathode ray tubes are described in the book entitled The Cathode Ray Tube and Its Applications by Parr and Davies published in 1959 and in numerous other texts.

The use of a phosphor introduces limitations in any recording system with particular reference to resolution, conversion efficiency, and limitations in dynamic range.

Prior art efforts to improve the efliciency with which information passes through the face plate of the cathode ray tube have followed three main paths. The first consists in improving the phosphor itself, the remainder of the system being unchanged. The other approaches involved strucural modification of the face plate, either by insertion of a Lenard window (see e.g. United States Patents 2,241,432 or 2,707,162) or by use of very fine wires passing from the inner face of the face plate to the outer face as shown in United States Patents 2,015,570 or 2,301,- 199, for example.

When the recording medium is passed across face plates modified in either of the above ways, rapid deterioration of the Lenard window, wire tips or record medium often result. These techniques also are limited in resolution by electron scattering in the window and by the wire spacing limitations in the cases of wired face tubes.

Another proposed improvement is described in United States Patent 3,222,678, issued December 7, 1965, to D. A. Jones. In this patent means are described for passing a web between an apertured shoe which corresponds to the target face of an electron gun and a shaped control member which maintains the web in its path. It has been found that the use of such a control member may increase the friction or drag on the web to an undesirable extent and may often cause the web to bind or seize during its passage over the surface of the shoe.

A principal object of this invention is to provide an electron beam recorder in which the electrons impinge directly on the record medium and which is free from the disadvantages experienced in prior art devices.

3,341,728 Patented Sept. 12, 1967 Another object of the invention is to provide a method in which the advantages of vacuum operation of a cathode ray tube are retained, but in which the film is available outside of the vacuum and in the normal atmosphere almost immediately after it has been exposed.

These and other objects of this invention will become more apparent from the description which follows and from the drawings accompanying this specification, in which FIGURE 1 is a schematic view of a complete recording system;

FIGURE 2 is an enlarged view of a detail of FIGURE 1; and

FIGURE 3 is a view in perspective of the detail of FIGURE 2 looking in the direction of the arrow.

As shown in FIGURE 1, paper, synthetic resin film, or other suitable record medium 10 passes from a supply spool 12 to a take-up spool 14 along a path which takes a it past the following in sequence: a vacuum hold down device, the face plate of a cathode ray tube 30, and a developing train 60.

The details of each of these stations depends on the specific record medium utilized.

In the present description the apparatus exemplified is used in connection with a film formulated by the application of carbon tetrabromide or other suitable organic halogen compound and N-vinyl carbazole or other N- vinyl compound or other amine to a support of paper, cloth or film forming plastic, suitable compositions being described in Wainer United States Patents 3,042,517, 3,042,516, and 3,042,515, each issued July 3, 1962, and other patents since issued on improvements thereover. The specific film composition and the modification of the film by addition of sensitizers, contrast intensifiers, etc. are all known, per se, and do not constitute the present invention.

The film passes from a supply reel 12 to a take-up reel 14 along a path which includes passage across the face of a cathode ray tube 30. The tube 30 includes the usual means 34 for deflecting and modulating the electron beam, and vacuum pump 36 to maintain a vacuum in the tube envelope 38. The tube has a face 40 having an arcuate shape across which the film is guided by rollers 42. Face 40 has a slit 44 defining an area at which the film is exposed directly to the electron beam. Preferably the slit is of a width which is sufficient to provide an adequate target area of exposed film and suificiently narrow that the film itself is held against the face of the cathode ray tube by the difference in pressure between the atmosphere pressing on its outer surface and the vacuum pulling its inner surface tightly against tube face 40. The dimensions of the slit and of other portions of the tube face are extremely important and the present invention is directed to means for insuring that the film remains in sufiiciently close contact with the tube face to insure that the vacuum in the tube is not seriously diminished while at the same time avoiding any binding or seizing of the film as it moves past the apertures in the tube face.

FIGURE 2 shows the means by which this result is secured. As shown in FIGURES 2 and 3, tube face 40 has a slit 44 which extends across only a portion of the width of face 40. Slit 44 is between a fraction (e.g. Mi) of a mil and mils and depends on the size of the electron beam in cathode ray tube 30 and the ability to machine a narrow slit in the face of the tube 30. Slit 44 is completely encircled by a vacuum frame 20 consisting of rubber or synthetic resin, or other material not chemically reactive with the film 10 passing across the face of the tube, and is preferably a material such as tetrafluoroethylene over which the film passes readily. Frame 20 has a front side 22 shaped to conform to the path taken by film 3 as it passes across face 40. The front side 22 of frame 20 is provided with a channel 24 having a rectangular configuration 50, 52 corresponding to slit 44 and completely surrounding said slit. Channel 24 is shown as rectangular for slit 44 which is rectangular, but both slit 44 and channel 24 could be of any other suitable shape provided channel 24 surrounded slit 44. Channel 24 is as narrow as possible, about or A being found to be quite satisfactory. With wider channels there is a tendency for very thin films to be sucked into the channel or to be bent or buckled by the vacuum applied to the channel. Channel 24 is spaced between 0.5 and 1.5 inches from the sides of slit 44 to insure that the film moving over slit 44 is fiat and is adequately supported by a plane area of the tube face. Channel 24 is connected by passage 26 to a manifold 28 which in turn is connected to a mechanical vacuum pump by means of tube 28.

Friction or drag when film 10 is pulled across frame 20 may be further diminished by coating the front side 22 of the frame with Teflon, Kel F, or a similar dry lubricant which can be baked onto face 22 and which has no tendency to accumulate in the slit 44.

It is also possible to apply a liquid or semisolid lubricant, such as a silicone, to the film 10 as it is unwound from reel 12 and before it passes across the face of tube 30, provided the amount of lubricant is not sufiicient to plug up either channel 24 or slit 44. Such lubricant provides a benefit in assisting in maintaining the vacuum seal between the film and the tube face.

The channel 24 surrounding the slit is evacuated with the aid of a rotary mechanical vacuum forepu mp. The evacuated channel holds the film in tight contact with the face plate, thereby providing a vacuum seal. This vacuum channel also serves somewhat in the function of an airlock by partially evacuating the region between the film and the end plate. I have found that, with an end plate constructed in this manner, it is possible to draw the film across the surface at film speeds up to 10 inches/ second while maintaining a vacuum of 5 lO torr or I better within the evacuated electron beam gun region. With the use of the vacuum channel hold-down, the requirements for lubricating the film is eliminated especially when the baked coating is used.

Because the vacuum is maintained at well below 1 1O- mm., the slit containing cathode tube operates substantially in the same manner as a cathode ray tube having a completely enclosed tube, evacuated to the usual degree.

The following example describes for purposes of illustration one specific manner in which the apparatus has been successfully employed in the production of clear sharp images on film of the type indicated.

Example A film was prepared by dissolving 20 grams of polyvinyl chloride, 20 grams of N-vinylcarbazole, and 14 grams of carbon tetrabromide in a solvent consisting of 80 milliliters of tetrahydrofuran plus 20 milliliters of acetone. The solution was coated on a 6 mil polyvinyl chloride film base with a wet coating thickness of 3 mils. The dried coating thickness was found to be approximately 1 mil. This film was utilized to record a line scan image using a cathode ray tube employing a 20 mil wide 2 inch long slit in the end plate. The electron beam diameter was 10 mils, the total beam current passing through the face plate was 10 microamperes, and the accelerating potential 20 kv. A high density recording was obtained at a film speed of 10 inches per second; the scanning rate of the electron beam in a horizontal direction being 1,000 scans per second. The equivalent charge exposure at any point on the film is readily calculated to be 0.1 microcoulombs/sq. cm. A variety of experiments indicate that this is near the minimum charge exposure required to provide a dense brown-black image. Information was recorded on the film by intensity modulating the electron beam during the scanning operation. The film was developed using radiant infrared radiation which served to heat the film to a temperature near 130 C. The time required for development was 2 minutes.

It is obvious that either higher resolution or higher recording speeds can be obtained by employing cathode ray tubes having smaller beam diameters or higher beam current densities respectively.

Although the above example describes the use of an organic heat-developed photochemical film as the recording medium, it will be apparent to others skilled in the art that this recording technique may be utilized with essentially any other electron beam sensitive recording media such as a conventional silver halide photographic I claim:

In combination, a cathode ray tube including an evacuated envelope, a face plate at one end of said envelope, said face plate having a slit between about 0.25 and mils in width, said slit extending through said face plate References Cited UNITED STATES PATENTS 11/1964 Stone 31373 12/1965 Jones 34674 JAMES W. LAWRENCE, Primary Examiner.

V. LAFRANCHI, Assistant Examiner. 

